At present, the door closer which installed on the top of the door or the floor spring which installed on the bottom of the door provided with a spindle on basement which can be connected to the door panel. Moreover, the spindle can control the rotational speed by the hydraulic mechanism, which accumulate preparatory pressure when the spindle rotated from the door opening. When the door is released, the door panel is slowly rotated to return to the closed position, because the hydraulic mechanism can provide a resistance to the return rotation of the spindle.
The hydraulic mechanism is generally provided with an adjustment valve, which can adjust the opening rate of the oil return passage for the oil in the hydraulic mechanism. It is thereby adjusting the flow rate of the oil to adjust the volume of the preparatory pressure which from oil accumulation and then control the speed of automatic return of the door panel.
However, the maximum angle of the opened door is between 90 to 180 degrees approximately, which means the distance from the spindle rotation by door panel is not long. The hydraulic mechanism must have the enough preparatory pressure from oil accumulation to resist the return rotation of the spindle by short distance from the spindle rotation. Even if the adjustment valve of the hydraulic mechanism is slightly adjusted, the preparatory pressure accumulated in the hydraulic mechanism is greatly changed, resulting in difficult to precision adjust the preparatory pressure, and so let the speed of the door closing too slow or too fast.
In addition, the pressure required to rotate the rest of the machine shaft is reduced by a much lower speed ratio after a gear shift. Therefore, the resistance pressure required for the medium is relatively low in the case of the same load. In the current market, because the floor spring or door closer operate with high pressure, if it's without strict quality control, it's easy to have leakage situation. Moreover, after a certain period of time, the high pressure is also easy to damage the oil seal and oil leakage, affecting the product life.